All or any of the parts of an induction coil may be purchased
ready-made, and the first thing to do is to decide which of the
parts the amateur mechanic can make and which would be better to
buy ready-made. If the builder has had no experience in
coilwinding it would probably pay to purchase the secondary coil
ready-wound, as the operation of winding a mile or more of fine
wire is very difficult and tedious, and the results are often
unsatisfactory. In ordering the secondary it is always necessary
to specify the length of spark desired.
The following method of completing a 1-in. coil illustrates the
general details of the work. The same methods and circuits apply
to small and larger coils. The ready-made secondary is in solid
cylindrical form, about 6 in. long and 2-5/8 in. diameter, with a
hole
[Illustration: Jump-Spark Coil]
through the winding 1-1/4 in. in diameter, as shown in Fig. 1. The
secondary will stand considerable handling without fear of injury,
and need not be set into a case until the primary is completed.
The primary is made of fine annealed No. 24 iron wire cut 7 in.
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